Molybdenum 99 (Mo-99) is a man-made radionuclide which decays (T1/2=66 hours) to Technetium-99m (Tc-99m). Tc-99m is a radioactive tracer isotope, frequently used in the nuclear medical field for diagnostic imaging. In the United States alone, it is used in about ⅔ of all diagnostic medical isotope procedures.
The use of Tc-99m in particular is beneficial for various reasons. Most importantly, it has a relatively short half-life of about 6 hours. This is especially ideal in medical diagnostic tests where the patient only retains a minimal amount of radiation from the examination while the radiologist is still able to attain thorough results quickly and efficiently. The metastable state of Tc-99m also ensures that the element will not transform into any other substance due to its own decay. Although, Tc-99 the decay product of Tc-99m is slightly unstable and can decay into ruthenium-99 and a weak beta particle, Tc-99 has a long half-life (T1/2=211,000 years). So the risk of decay and damage to the body from Tc-99 is minimal.
When Tc-99m decays, it emits a 140.5 keV gamma ray. The wavelength of this gamma ray is ideal for medical imaging. The single gamma ray without the presence of beta emission is advantageous for enhanced medical imaging.
Tc-99m is produced solely from the gamma decay of Molybdenum-99 (Mo-99). Due to Mo-99 having a relatively short half-life, it cannot be stored for an extended period of time. It must be continuously made, particularly because it is in such high demand.
Currently there are a limited number of (fission reactor) facilities producing Mo-99; any disruption of these facilities' operations can have severe effects on the supply chain and ultimately patient care. Additionally, producing the material via the fission process generates radioactive waste which is expensive to manage and dispose of.